The best view of what Katherine Boo calls the “overcity” is to be found on the roof deck bar at the top of the Four Seasons hotel, 34 floors above midtown Mumbai. It is a flashy place, full of glass partitions and uncomfortable white furniture, where crowds of ex-pats and well-heeled locals drink thousand-rupee (about $20) cocktails. In the distance you can make out the 27-story silhouette of billionaire industrialist Mukesh Ambani’s new home, Anitilia, a residential skyscraper built a few years back at an estimated cost of $1 billion—one of the most expensive homes ever constructed. Next door to the hotel there is a slum. The last time I visited at dusk, I looked down to see smoke rising from many dozens of tightly packed shanties. But once night falls, it is barely visible.

Other high-rises dot the horizon of an area once dominated by textile mills and industrial plants, new homes for the banks and brokerages that embody Mumbai’s aspiration to challenge Singapore and Hong Kong someday as Asia’s financial capital. Peer between them to the north and you can just about make out the city’s “sea-link” bridge, a rare piece of newly built infrastructure running up the left side of the peninsula. It cuts the time to reach the airport by around 30 minutes, although at 50 rupees (or about $1), the toll is much too expensive for most Mumbaikars.

This is a panorama of what author Sukheta Mehta christened the “Maximum City”—a sprawling metropolis with a population edging close to 20 million, whose vibrant mixture of commercial possibility and Bollywood glamour plays much the same role in the imagination of aspirant Indians as New York or Los Angeles does in the United States. It is also a vision of what is often known as “the new India,” a partly mythic country found in Harvard Business School case studies and the columns of Thomas Friedman: a nation of business parks, clever software developers, and efficient outsourcing businesses. Twenty years ago India opened its economy to the world. This is the result.

All this is not the real focus of Boo’s revealing book, whose subtitle is “Life, Death, and Hope in a Mumbai Undercity.” But the geography of India’s most glamorous metropolis—its elite neighborhoods, five-star hotels, and slum-surrounded airport—is a constant presence. Just as the Four Seasons was built on land reclaimed from a slum, so the lives Boo describes, of Mumbai’s most downtrodden, are at once distant from and inextricably linked to the fast, global, and partly prosperous city on which they squat.

Boo is a journalist best known for highlighting the plight of America’s poorest, most notably in The New Yorker, where her style of thickly descriptive and deeply compassionate writing about the inner lives of the underprivileged has won widespread admiration. It also saw her pick up a Pulitzer Prize in 2000 while at The Washington Post for articles examining neglect in homes for the developmentally disabled. But having come to India late in life—she fell in love with an Indian academic, as she explains in an afterword—Boo, 47, found the questions of injustice and poverty that informed her writing in America laid out even more starkly.

Unlike most books written by foreigners on the subcontinent, Behind the Beautiful Forevers is narrowly focused. Boo paints a portrait of just a handful of characters in a small corner of one city, rather than a sweeping tableau of the nation. But for that it is one of the sharpest and most urgent critiques of the country’s model of development, and the failures of its political and business elites to keep pace with the rising aspirations of India’s more than one billion citizens.

Behind the Beautiful Forevers details the three or so years Boo spent visiting Annawadi, a small slum perched on the edge of the international airport. As she explains early on:

Annawadi sat two hundred yards off the Sarah Airport Road, a stretch where new India and old India collided and made new India late. Chauffeurs in SUVs honked furiously at the bicycle delivery boys peeling off from a slum chicken shop, each carrying a rack of three hundred eggs. Annawadi itself was nothing special, in the context of the slums of Mumbai. Every house was off-kilter, so less off-kilter looked like straight. Sewage and sickness looked like life.

Annawadi is a name virtually no one outside its neighborhood would have heard of. Visitors to Mumbai might chance to see its rooftops from their windows as they fly in. But this is a hamlet of around 3,000 people in 335 dwellings, in a city where a single slum can house hundreds of thousands—in one case, perhaps more than one million. That the lives Boo catalogues are both unremarkable and anonymous is part of the power of her story.

Boo lived in Annawadi for long periods, shadowing and attempting to understand its residents, often in arduous conditions. At first the slum-dwellers would point her toward the nearby hotels, worried that she was lost. But she hung around long enough to fade into the background, and put together a rich and textured picture of those living there.

The narrative picks out the lives of a handful of these residents as they struggle for minor material advancement. The first are the Husains, a Muslim family of garbage pickers, working as part of the recycling supply chain that provides employment for many slum-dwellers, and in particular their eldest teenage son:

Avoid trouble. This was the operating principle of Abdul Hakim Husain, an idea so fiercely held that it seemed imprinted on his physical form. He had deep-set eyes and sunken cheeks, a body work-hunched and wiry—the type that claimed less than its fair share of space when threading through people-choked slum lanes…A modest, missable presence was a useful thing in Annawadi, the sumpy plug of slum in which he lived.

As this passage makes clear, Boo’s style is literary, almost novelistic. She provides Abdul, his parents and siblings, and the book’s other characters with detailed and moving interior lives, drawn from a combination of observation, interviews, and her own perception. The result is an often horrifying but also deeply human account of the daily insecurities of slum life, quite unlike any that I have read.

Yet the book is as interesting for its substance as much as its style. True, for a work of nonfiction it is strikingly nonjudgmental. In 250 or so pages there are few explicit opinions, and the author avoids anything that might be described as policy prescriptions for improving the bleak conditions she describes. Nonetheless there are a number of arguments underlying Behind the Beautiful Forevers, even if the author makes them obliquely. This is a more political book than it first appears.

Her first argument concerns the setting. In recent years slums have undergone something of an intellectual renaissance. The likes of Harvard economist Edward Glaeser and environmentalist Stewart Brand have published books that try to turn around the traditional images of slum housing as hellish and intolerable. The revisionist account points out that people move to slums voluntarily because they are economically vibrant and socially supportive—a bottom rung on a ladder that can lead to social advancement. There is an undeniable logic to this view. Mankind’s future is urban. Estimates suggest India’s cities will double in population from 300 million to around 600 million in the next two decades or so. Mumbai, already absurdly crowded, will grow to something north of 30 million. Many of these newcomers will live in slums, and there is little that can realistically be done to reverse this tide of human migration. Despite well-meaning attempts to revitalize the countryside of nations like India and China, rural residents there know that economic opportunity and a degree of social freedom are to be found only in cities, and they vote with their feet. Nonetheless any description of slums is problematic if it downplays the problems that lie within them. This is Boo’s first argument: Slum life contains richness and complexity, but it remains extraordinarily unjust.

The theme plays out throughout the tragedy that lies at the heart of her book. As the narrative begins, Abdul is cowering inside his garbage storage shed, having fled the scene of an argument between his family and a neighbor. The spark was a decision to improve part of their tiny family home. Abdul frets about the move, thinking it will attract envy and attention. His concerns are borne out when a quarrel over the work spins out of control, and an angry neighbor retaliates by setting herself on fire: “The brothel keeper was the first across the maidan, three boys fast behind, throwing their weight across the door until it broke. They found Fatima thrashing on the floor, smoke pouring off her skin. At her side was a yellow plastic jug of kerosene.”

The grim chain of events that follow is partly about injustice in a literal sense, as Fatima, a disabled woman known in the slum as “One Leg,” accuses Abdul’s family of burning her. The police get involved, mostly because crimes provide an excuse for extortion. The family is plunged into the brutality and petty corruption of India’s local law enforcement, and eventually its courts, a world in which “the most wretched tried to punish the slightly less wretched by turning to a justice system so malign it sank them all.”

More generally, however, Boo’s concern is the broader injustice of slum life that comes with being overcome with bad luck. In a slum, even minor ructions can have profound consequences: Fatima ends up in a hospital where she dies for lack of medicine; Abdul and his father both land in prison while their family pitches into a desperate struggle against the malignant authorities. As Boo notes, again describing Abdul, the lives of residents are marked by their precariousness as much as their brutality:

It seemed to him that in Annawadi, fortunes derived not just from what people did, or how well they did it, but from the accidents and catastrophes they dodged. A decent life was the train that hadn’t hit you, the slum lord you hadn’t offended, the malaria you hadn’t caught.

The travails of the Husains bring about the book’s second focus: corruption, and thus also politics. That India has a corruption problem is no secret. There are numerous lurid stories of tycoons and politicians trading suitcases of cash for regulatory advantage, most famously the 2008 scam over the allocation of second-generation mobile-telephone licenses, which by some estimates cost the country $39 billion. Far below that lies an epidemic of more humdrum day-to-day bribery, the spark for last year’s nationwide anti-corruption protests. For all that, however, the reality of India’s system of corruption and how it infects its democracy is more mysterious. Yet Boo manages to provide genuine insight, especially in the book’s most intriguing character, Asha, a local matriarch attempting to clamber her way out of the slum through political advancement.

In the West, and among some in the Indian elite, this word, corruption, had purely negative connotations; it was seen as blocking India’s modern global ambitions. But for the poor of a country where corruption thieved a great deal of opportunity, corruption was one of the few genuine opportunities that remained.

Asha makes her living in “the fixing business” by mediating the disputes of her neighbors. In return she ensures they turn out to vote for her elected masters, a role to which she ultimately aspires. Asha is especially adept at manipulating the assistance of Western charities. Female empowerment self-help groups are concocted to impress foreign visitors, complete with inspiring crescendos about slum girls going to college. Sham slum schools are established, including one run by her well-meaning daughter, who vexes Asha by providing lessons rather than just taking the money.

In the end, however, Asha is the only figure in Boo’s book to escape the gravity of the slum’s misfortunes. One of her shell NGOs proves useful to a corrupt government official as a conduit through which to siphon money supposedly destined for education projects. She finds herself with enough money to buy her daughter a computer and gives up on her political machinations. As the director of a charity, she achieves her ambition: She becomes, in Boo’s words, a “member of the overcity.”

Yet elsewhere, virtually all the other characters emerge smaller and sadder. Abdul Husain manages to avoid prison on trumped-up murder charges, but loses most of his business, and with it his family’s hopes of escape. Others trudge on; a handful of characters die at their own hands. The slum itself may be bulldozed for redevelopment: In front of it, the large outdoor advertising sign for Italian-style floor tiles with “beautiful forever” repeated across—which gives the book its title—has already been knocked down.

Behind this grim and unredeemed story lies an important academic debate over the success or otherwise of India’s development. On one side stand economists like Jagdish Bhagwati, who argue that for all its difficulties the country is making progress: Tens of millions are being lifted out of poverty and gaining access to education or basic consumer goods. On the other are figures like Nobel laureate Amartya Sen, who take a less sanguine view, pointing instead to India’s growing inequality and the fact that many basic development indicators are gradually falling behind poorer neighbors like Bangladesh and Nepal.

Despite her unwillingness to delve into politics or to conclude with anything like a set of recommendations, Boo is clearly on Sen’s side. You can’t imagine her having much time for the Thomas Friedman vision of India’s rise. And as she says, caustically, right at the start of the book: “Almost no one in this slum was considered poor by official Indian benchmarks. Rather, the Annawadians were among roughly one hundred million Indians freed from poverty since 1991.”

She concludes by locating those she has observed in a larger picture of poverty and globalization, placing the struggles of Mumbai’s poorest alongside those of Nairobi and Rio, even New York. In doing so, she reveals a rather traditional progressive political perspective, with a yearning for solidarity and mutual support. But in the end, Boo’s warning is specifically Indian. Some here see the extraordinary wealth and corruption that have followed the nation’s two decades of economic openness as a passing phase, not much different from Britain in the eighteenth century and America in the late nineteenth century. On this reading contemporary Mumbai is just a respun Dickensian London, or turn-of-the-century Chicago—a metropolis blighted by weak governance, speedy urbanization, and fast-changing capitalism, but one that will grow out of it in time.

There is some merit to this view, but it is also presumptuous. True, you hear more about corruption in India than in China in part because it is a democracy. The media here are exuberant and relatively free. There exists a range of well-respected and broadly honest institutions, in particular the upper echelons of the judiciary. (The lower courts, as Boo shows, are less reliable.) As a consequence the political system has reacted to public anger over corruption in recent years: Trials rumble on; new anti-graft laws are promised; one minister has been jailed. There is at least a debate about India’s future, even if one mixed in with general resignation over the capacity of its political and business elite to deliver.

Some of the current gloom is also cyclical. Over the last year, India’s economy has slowed sharply. Leaders once talked excitedly of annual growth of 9 or even 10 percent. This now seems fantastical. A mixture of weak political leadership, high interest rates, and plunging industrial investment has seen growth fall to nearer 6 percent. This sounds fine enough to most Western ears, but in a still very poor country with a fast-growing population and precarious public finances, most economists think it isn’t enough.

Yet there are also deeper problems with the nation’s governance and commerce that lie behind the world Boo describes, just as Annawadi hid behind the “beautiful forever” sign. India’s state is at once too weak and too intrusive. The economy remains dominated by a mixture of inefficient public-sector industries and sprawling family-controlled industrial houses. The latter have been the source of much of the graft that pervades India’s politics. A rotten system of mutual interdependence has grown up in which the state relies on the tycoons to develop the economy, while political parties, in the absence of a system of state funding, need kickbacks to fund the workings of the world’s largest democracy. The result has been neither efficient nor equitable.

This system has been challenged somewhat over the last couple of years by public concerns over corruption, but only to the extent that it is now more difficult to be seen openly giving favors to the well-connected, for instance by doling out licenses to develop land or explore for natural resources. This is part of what has gummed up the workings of the state, slowing growth and investment. The phrase “political paralysis” is now often heard here to describe a situation in which anxious bureaucrats and party leaders cover their backs and little gets done.

Historian Ramachandra Guha makes the point that visitors to India have for generations come to the conclusion that the nation is basically unworkable: Its geography is too vast; its population too diverse, and its politics too quarrelsome. Yet for all its imperfections, it has survived—overcoming imperialism, partition, and endemic poverty to create a democracy that, while far from perfect, bears favorable comparison to, for instance, China. The hope is that with further reform, the nation’s economic progress will eventually be more broadly shared; that the undercity and overcity will come together. But at present it remains just a hope. There are plenty of signs that India’s future is just as likely to resemble the crony capitalism and deformed democracy of Russia. This is India’s own Gilded Age, and Katherine Boo has sounded the loudest warning about its failings.